1. Field of the Invention
The present invention relates to a motor controller and a construction machine provided with the motor controller.
2. Description of the Related Art
Conventionally, various techniques concerning the securement of maintainability have been proposed for an operating machine or the like, the drive mechanism of which is partially motorized. For example, the operating machine disclosed in Japanese Patent Application Laid-Open Publication No. 2010-202135, when shut down, decouples a battery from a DC bus by switching operation and drives only a motor for cooling apparatus making use of electric charges from a capacitor connected to the DC bus. Consequently, the capacitor is discharged without rotating a motor for an engine. Accordingly, the voltage of the DC bus decreases to a harmless level even if a maintenance operator comes into contact with the DC bus.
In such a configuration as described above, however, discharge is not possible if the motor for cooling apparatus fails. In addition, such a configuration as described above is not applicable to operating machines without any cooling apparatus. On the other hand, Japanese Patent Publication No. 3225771 discloses a configuration in which a battery is discharged using a motor for vehicle travel, rather than a motor for cooling apparatus. In the configuration disclosed in Japanese Patent Publication No. 3225771, a given d-axis current is determined on the basis of the electric angle of the motor for vehicle travel and the battery is discharged with the motor in the stopped state by supplying only the d-axis current to the motor.